Numerous cationic species which initiate the copolymerization of formaldehyde with cyclic ethers are known in the art. The practical problems associated with copolymerization of formaldehyde and cyclic ethers involve attaining high molecular weight, minimal by-products, and effective incorporation of the cyclic ether monomer into the polymer.
BF.sub.3 -etherate initiators are the best known in the art for initiating polymerization of cyclic acetals or ethers, including copolymers. See for example Encyclopedia of Polymer Science and Engineering, 2nd ed., Wiley, New York, c1985. However, use of BF.sub.3 -etherate in the copolymerization of formaldehyde and cyclic ethers requires undesirably large equilibrium concentrations of the cyclic ether in the reaction medium, aggravating problems of waste disposal and necessitating recycling.
Strauss, Chemical Reviews, vol. 93, pp 927ff (1993), identifies the tetraphenylborate anions, and particularly the fluoro-substituted tetraphenyl borates, as particularly useful counterions for catalyzing olefin polymerizations because of the combination of very weak coordination, high stability, and an absence of strong basic sites on the periphery. Fluoro-substituted tetraphenyl borates and derivatives are disclosed as being more weakly coordinating anions than, among others, SbF.sub.6 -, AsF.sub.6 -, PF.sub.6 -, and BF.sub.4 -.
Jia et al., Organometallics, vol. 16, pp. 842ff (1997) disclose metallocene olefin polymerization catalysts based upon counterions of tetrakis(pentafluorophenyl)borate and its derivatives. Cationic catalysts based thereon exhibit higher activity and better stability than the corresponding catalysts based upon Me(C.sub.6 F.sub.5).sub.3 -, where "Me" is methyl. Further disclosed is improved solubility in non-polar solvents of tetrakis(pentafluorophenyl)borate based counterions when lipophilic, sterically hindered, p-electron withdrawing groups are substituted on the aromatic rings. Exemplified are substitution of tert-butyldimethyl silyl or triisopropylsilyl for one of the fluorines in each aromatic ring. The unsubsituted tetrakis(pentafluorophenyl)borate was the most weakly coordinating, although the activities of the substituted species were higher.
Chen, Journal of Polymer Science, vol. 14, pp 129ff (1976), discloses copolymerization of trioxane and ethylene oxide to form polyoxymethylene copolymer catalyzed by p-chlorophenyl diazonium cations complexed with hexafluoro anions formed from Group VA elements including phosphorous, arsenic, and antimony. It is disclosed that the nature of the anion controls the chain transfer process as well as propagation and side reactions. p-Chlorophenyl diazonium hexafluoroantimonate was found to produce numerous side reactions and polymer of low molecular weight while the arsenate yielded high molecular weight and few side reactions.
Kedrina et al., Polymer Science, vol. 33, pp. 799ff (1991) disclose copolymerization of formaldehyde with 1,3-dioxolane to form polyoxymethylene copolymers. Comparison is made between BF.sub.3 -etherate catalyst and perfluoroalkane sulphonic acids. Reacting in hexane, PFSA was found to be more selective for dioxolane than BF.sub.3 -etherate. At 0.75 mol/l of dioxolane using PFSA catalyst, polymer containing greater than 7 mol-% dioxolane having a number average molecular weight greater than 6.times.10.sup.5 was formed. Polymer having ca. 3 mol-% dioxolane was formed at dioxolane concentration of ca. 0.25% dioxolane, resulting in polymer of ca. 2.times.10.sup.5 molecular weight.
Kubisa, Polimery, vol. 21, pp. 393ff (1976) discloses homopolymerization of dioxolane using triphenyl methyl (trityl) cations complexed with SbF.sub.6 -, SbCl.sub.6 -, AsF.sub.6 -, and BF.sub.4 -.
Brown, German Preliminary published application No. DT 2 006 457 (1970), achieves high rates of incorporation of dioxolane in copolymerization with formaldehyde at high molecular weights using antimony hexafluoride counterion with a number of cations including triethyloxonium and triphenylmethyl carbenium.